1. Field of the Invention
The present invention relates to processes for preparing novel catalysts comprising an iron compound and a bisphosphine compound, and to processes for producing aromatic compounds by coupling halogenated hydrocarbons and aromatic metal reagents using these catalysts.
2. Description of Related Art
Alkylated aromatic compounds, and in particular, a class of aromatic compounds having secondary alkyl groups on their aromatic rings, are known to be useful as starting materials for liquid crystals, or as chemical intermediates for pharmaceuticals, agrochemicals, and the like.
Recently, research into cross-coupling reactions between alkyl halides and aromatic metal reagents is actively taking place. In particular, reports have been made on cross-coupling reactions using iron catalysts, which are inexpensive and readily available (e.g., Non-Patent Documents 1-8, and Patent Document 1).
For example, Patent Document 1 and Non-Patent Document 7 disclose processes wherein cross-coupling reactions between alkyl halides and aromatic magnesium reagents are conducted in the presence of iron (III) chloride and N,N,N′,N′-tetramethylethylenediamine (TMEDA). However, these processes require a relatively large proportion, i.e., about 5 mol %, of the iron catalyst relative to the alkyl halide, which is the substrate; therefore, there is still room for improvement in terms of cost and reaction efficiency. Furthermore, substitution of aromatic rings with fluorine atoms is often carried out from the viewpoint of imparting a variety of functionalities to cross-coupling compounds. However, this method is not sufficient for producing a variety of functional compounds because cross-coupling reactions do not proceed at all when using aromatic magnesium reagents having fluorine atoms on their aromatic rings.
Non-Patent Document 8 discloses a process wherein a cross-coupling reaction between an alkyl halide and an aromatic zinc reagent is conducted in the presence of iron (III) chloride and 1,2-bis(diphenylphosphino)benzene (DPPBz). This process also requires a relatively large proportion, i.e., about 3 mol %, of the iron catalyst relative to the alkyl halide; therefore, there is still room for improvement in terms of cost and reaction efficiency.
For these reasons, there has been a need for a process that does not place limitations on the structure of the substrate, and that can efficiently produce a variety of cross-coupling compounds.    Patent Document 1: WO 2005/075384    Non-Patent Document 1: Org. Lett., 6, 1297 (2004)    Non-Patent Document 2: Angew. Chem., Int. Ed., 43, 3955 (2004)    Non-Patent Document 3: J. Org. Chem., 71, 1104 (2006)    Non-Patent Document 4: Angew. Chem., Int. Ed., 46, 4346 (2007)    Non-Patent Document 5: Angew. Chem., Int. Ed., 47, 1305-1307 (2008)    Non-Patent Document 6: Synlett, 1794 (2005)    Non-Patent Document 7: J. Am. Chem. Soc., 126, 3686-3687 (2004)    Non-Patent Document 8: Chemical Society of Japan, Proceedings of the 87th Annual Spring Meeting, 1D8-12